Plasma display panel having coplanar electrodes with constant width

ABSTRACT

Panel comprising an array of barrier ribs each having a base resting on a plate and a top in contact with another plate that includes at least two arrays of coplanar electrodes each preferably having a constant width. According to the invention, these barrier ribs have, at their top, a low-permittivity region of thickness greater than 3 μm and less than or equal to one fifth of their total height, which has a mean dielectric permittivity at least three times smaller than the dielectric permittivity of these barrier ribs measured at their base. Thanks to the invention, the confinement of the plasma discharges far from the barrier ribs is substantially improved.

This application claims the benefit, under 35 U.S.C. §365 ofInternational Application PCT/EP03/50639, filed Sep. 18, 2003, which waspublished in accordance with PCT Article 21(2) on Apr. 22, 2004 inFrench and which claims the benefit of French patent application No.0212931, filed Sep. 27, 2002.

BACKGROUND OF THE INVENTION

The invention relates to a plasma display panel comprising, as shown inFIGS. 1A, 1B, a first plate 11 and a second plate 12 leaving betweenthem a space filled with a discharge gas and compartmentalized into anumber of discharge cells 18 arranged in rows and columns, which alsoincludes an array of insulating barrier ribs comprising barrier ribs 15each separating two adjacent columns of cells, the first plate includingat least two arrays of coplanar electrodes Y, Y′ called sustainelectrodes, which are oriented in general directions that are parallelto one another and perpendicular to said barrier ribs, having a constantwidth perpendicular to these general directions, and are arranged insuch a way that each discharge cell is traversed by an electrode of eacharray.

Since the barrier ribs 15 each separate two adjacent columns of cells,these barrier ribs are called column barrier ribs, as opposed to rowbarrier ribs described later.

Each discharge cell is therefore traversed by a pair of sustainelectrodes and each pair of sustain electrodes therefore supplies a rowof discharge cells; all the adjacent cells of any one row are separatedby a column barrier rib made of insulating material; in this way, in thegeneral direction of the coplanar electrodes, the widths of the variouscells in any one row are limited by these column barrier ribs. Thesebarrier ribs generally serve as spacers between the plates of the panel.

The coplanar electrodes are covered with a dielectric layer 13 which isitself coated with a protective/secondary-electron-emissive layer 14,generally based on magnesia.

The second plate includes a third array of electrodes X called addresselectrodes, each placed between two column barrier ribs. Thus, eachaddress electrode therefore supplies a column of discharge cells. Theseaddress electrodes may also be covered with a dielectric layer 17.

The array of barrier ribs in certain panels of the prior art alsoinclude barrier ribs 16 called row barrier ribs each separating twoadjacent rows of cells, in such a way that each cell of the panel istherefore bounded, over its entire perimeter, by barrier ribs as shownin FIGS. 1A, 1B.

The operation of driving the plasma panels conventionally includesaddress periods intended to activate those cells that have to be turnedon, followed by sustain periods during which series of sustain voltagepulses are applied between the sustain electrodes Y, Y′ supplying a rowof cells, and the gap G separating these electrodes. The amplitude ofthese sustain pulses must be sufficient to cause discharges in thosecells in the row that have been actuated beforehand but insufficient tocause discharges in the cells of this row that have not been activatedbeforehand.

The addressing of the discharge cells generally takes place between acolumn electrode and one of the row electrodes, which also serves forsustaining.

The discharge cells and the space between the plates are filled with alow-pressure gas suitable for obtaining discharges that emit ultravioletradiation.

The walls of each cell are generally provided with a layer of a phosphorcapable of emitting visible radiation, especially in the red, green orblue, when it is excited by the ultraviolet radiation of the discharges.These layers are generally deposited on the second plate and on the sidewalls of the barrier ribs.

In the case of panels emitting three primary colors, namely red, greenand blue, these adjacent discharge cells have phosphors of differentcolors so that discharges emitting indirectly in the red, the green andthe blue are obtained.

It is in general the first plate, the one bearing the coplanarelectrodes, which serves as the front plate turned toward the personobserving the images that the panel is capable of displaying. To preventthe electrodes of the front plate absorbing too great a portion of thevisible radiation coming from the cells, the coplanar electrodes arepreferably made of a material that is both conductive and transparent,such as tin oxide or mixed indium tin oxide (ITO); as these transparentelectrodes are not in general conductive enough, the arrays oftransparent electrodes are generally “duplicated” with opaque metalconductors, called “bus conductors” since they distribute the electricaldischarge current to the transparent electrodes. Conventionally, thelinear electrical conductivity of the bus is greater than that of theinitiating conductor. The bus is made of a highly conductive metallicmaterial, such as silver, and consequently it is opaque to light.

During a sustain period, when an electrical voltage pulse of sufficientamplitude is applied between two coplanar electrodes Y, Y′ of any onepair, in a cell supplied via these electrodes and activated beforehandduring an address period, a discharge is initiated in the gap G near theinitiation edge 191 of one of these electrodes, over a front thatextends between the column barrier ribs 15 that define, widthwise, thiscell at this point. As shown in FIG. 1A, the discharge is initiated inthis cell in an initiation region Z_(a) of the portion of this electrodethat corresponds to this cell. It is preferable for the surfacepotential properties of the dielectric layer 13 coating this electrodeto be sufficiently uniform to allow initiation of the discharge at lowvoltage. After initiation, the discharge spreads out perpendicular tothe general direction of the coplanar electrodes as far as theend-of-discharge edge 192 of the electrode, on the opposite side fromthe initiation edge. The phase during which the discharge spreads out,called the expansion phase, allows the formation of a discharge regionwith a low electric field, this being very effective for exciting thegas and producing ultraviolet photons. The expansion phase thereforeimproves the luminous efficiency of the discharges. During the expansionphase, when the discharge expands up to the end-of-discharge edge of theelectrode, the discharge occupies almost all of the gas space bounded bythe two column barrier ribs 15 that define the width of the cell.

During a sustain period, immediately before an electrical voltage pulsehas been applied between two coplanar electrodes Y, Y′ of any one pairtraversing a cell, the dielectric layer region that covers theseelectrodes is generally covered with residual charges called “memorycharges”, coming in particular from the previous discharge in that cell.Immediately at the start of application of an electrical voltage pulseand before any new discharge, the discharge gas region lying betweenthese two electrodes is then subjected to the sum of the voltage appliedbetween these electrodes and of the voltage resulting from the memorycharges coming from the previous sustain pulse.

FIG. 3 shows, at the start of a sustain voltage pulse of 100 V amplitudeapplied to the electrodes, which follows from other identical AC pulsesthat have left memory charges, the distribution of the equipotentialvoltage lines in a cross section on A1-A1′ of the discharge expansionregion, between the middle of a column barrier rib 15 and the middle ofthe cell, this range corresponding to half the distance between thecenters of two adjacent column barrier ribs, that is to say thehalf-width of a discharge cell. The equipotential lines, shown ascontinuous lines, correspond to positive values of the potential whilethe equipotential lines shown as broken lines correspond to negativevalues of the potential. The potential difference between two adjacentequipotential curves is constant and suitable for obtaining twenty“positive” equipotential curves shown as continuous lines. During theinitiating 100 V voltage pulse, it is assumed here that the electrode inquestion, Y, acts as cathode and that the negative memory charges storedin this cell on the surface of the dielectric layer 13 come from thedischarge generated by the previous sustain voltage pulse of the sameseries, but of opposite sign. In this figure, the equipotential curve Vcorresponds to the first negative equipotential (shown in broken lines,as opposed to the continuous lines of the positive equipotentials) andindicates the presence of a negative charge deposited at this point onthe surface of the column barrier rib 15. The distribution of thisequipotential depthwise in the column barrier rib indicates that, afterinitiation caused by the pulse in question, the discharge will spreadout over the side walls of the barrier ribs, and therefore beyond thesurface of the dielectric layer 13 and the protection layer 14 coveringthe electrode Y. During sustain periods in which the panel emits light,the barrier ribs will therefore be in substantial contact with thedischarges. This phenomenon results in bigger losses of the chargedspecies on the barrier ribs and to accelerated deterioration of thephosphor material covering these barrier ribs with, as a consequence, areduction in the luminous efficiency and a reduction in the lifetime ofthe panel.

The prior art, illustrated for example by document EP 0 782 167(PIONEER), proposes a solution to this problem that is shown in FIG. 2.FIG. 2 shows a schematic top view of the structure of a cell of acoplanar plasma display panel that differs from the structure shownpreviously in FIGS. 1A and 1B in that the coplanar electrodes no longerextend over the entire width of the cells. Each electrode Y includes acontinuous conductive bus Y_(b) at the end-of-discharge edge 192 thattraverses all the cells of any one row and, in each cell, an electrodeelement Y_(p) in the form of a tongue centered on this cell, having awidth smaller than this cell and extending from the bus as far as theinitiation edge 191. The electrode elements Y_(p) of each cell are sizedin such a way that their lateral edges are positioned at a non-zerodistance D from the surface of the closest column barrier ribs 15 thatdefine this cell.

Such a structure applied to the coplanar electrodes Y, Y′ makes itpossible to reduce the potential on the side walls of the column barrierribs and on the surface portions of the protective layer that are closeto these barriers along the lateral edges of the electrode elementsY_(p), as illustrated in FIG. 4, which shows the distribution of theelectrical equipotential curves in the cell shown in FIG. 2, in a crosssection on A2-A2′ in the mid-width of the cell, and of the sameassumptions and conventions as for FIG. 3 described above. This FIG. 4indicates that the first negative equipotential curve, shown in brokenlines, meets the V-shaped column barrier rib at the top of this rib, atthe interface with the protective layer and the dielectric layer 13.

It follows from these dielectric properties, illustrated by theequipotential curves, that there is better confinement of the sustaindischarges away from the column barrier ribs at the start of expansionin the panels described in document EP 0 782 167 or, with reference toFIG. 2, relative to the panels described previously with reference toFIGS. 1A and 1B. Thus, the luminous efficiency and the lifetime areimproved.

However, at the end of expansion of the discharges, that is to say atthe buses Y_(b) of the coplanar electrodes, the same problem aspreviously is encountered since the electrodes extend at this point overthe entire width of the cells. The potential along the barrier ribsurface and the surface of the protective layer remains high near theelectrode portions Y_(b) corresponding to the buses. The improvement inluminous efficiency and in lifetime therefore remains limited.

Furthermore, such a structure having electrode elements is moredifficult to produce than that of FIGS. 1A and 1B and requires anexpensive operation of horizontal alignment of the plates 11 and 12 sothat the electrode elements specific to each cell are perfectly centeredon each cell and equidistant from two adjacent column barrier ribs.

SUMMARY OF THE INVENTION

The object of the invention is to increase the luminous efficiency ofplasma panels and their lifetime by avoiding these limitations and thesedrawbacks.

For this purpose, the subject of the invention is a plasma display panelcomprising a first plate and a second plate leaving between them a spacefilled with a discharge gas and partitioned into a number of dischargecells that are arranged in rows and columns, which also includes anarray of insulating barrier ribs comprising barrier ribs each separatingtwo adjacent columns of cells and each having a base resting on the saidsecond plate and a top in contact with the said first plate, this firstplate including at least two arrays of coplanar electrodes Y,Y′ calledsustain electrodes, which are oriented along general directions that areparallel to one another and to the said rows, which are placed so thateach discharge cell is traversed by an electrode of each array,therefore forming a pair, and which have edges called initiation edgeswhich face one another on either side of the gap separating theelectrodes of each pair, characterized in that each column separationbarrier rib comprises, at its top and over its entire width, asuccession of low-permittivity regions that extend at least on each sideof the gap separating the electrodes of each pair, at least startingfrom a line located 80 μm to the rear of the initiation edges of theelectrodes of this pair, and which have a thickness of greater than 3 μmbut not exceeding one fifth of the total height of the said barrierribs, and a mean dielectric permittivity at least three times smallerthan the dielectric permittivity of the said barrier ribs measured attheir base.

The low-permittivity regions thus extend over at least each side of thegap of each cell.

The thickness of a low-permittivity region on a barrier rib is measuredfrom the top of this rib in contact with the first plate. Each of theseregions extends approximately over the entire width of the barrier ribto within the thickness of any phosphor layer.

If the coplanar electrodes not of constant width, for example as in thestructure of the prior art described with reference to FIG. 2, theinvention then makes it possible to combine the efficiency advantagesalready described in this structure with those specific to the inventiondescribed below.

The invention applies especially to cases in which the coplanarelectrodes each have a constant width over their entire useful length.The term “useful length” of an electrode is understood to mean thelength corresponding to all of the cells served by this electrode. Thewidth of this electrode is understood to mean the width measuredperpendicular to its general direction. Since the width of the coplanarelectrodes is constant in the structure of the prior art described withreference to FIGS. 1A and 1B, the arrays of electrodes are lessexpensive to produce and the operation of assembling the plates is notpenalized by alignment constraints. Thus, the drawbacks of the structureof the prior art described with reference to FIG. 2 are avoided, whileobtaining at least equivalent if not better advantages from thestandpoint of luminous efficiency and lifetime, as will be explainedbelow.

The invention specifically aims to modify the distribution of theequipotential curves not by modifying the shape and position of theelectrodes in each cell, as described previously with reference to FIGS.2 and 3, but by varying the dielectric permittivity within the barrierribs in a manner suitable for making, in each cell, the equipotentialcurves near the dielectric layer and the protective layer closertogether and so as to reduce the electrical potential on the side wallsof these barrier ribs, especially near these layers.

Thanks to the thickness specific to the invention of thelow-permittivity regions and thanks to the mean dielectric permittivityspecific to the invention of these regions, there is therefore betterconfinement of the sustain discharges over the surface of the dielectriclayer and of the protective layer, away from the barrier ribs, therebyreducing the loss of charged species from the plasma and the degradationof the phosphors on these barrier ribs by the plasma in the dischargeexpansion region.

An additional advantage of the structure of the panel according to theinvention results from obtaining the desired confinement of thedischarges even at the end of expansion. Unlike the structure describedwith reference to FIG. 2, the potential on the side walls of the barrierribs and at the surface of the protective layer and of the dielectriclayer is also lowered near the electrode portions corresponding to theend of discharge. This allows even greater improvement in the luminousefficiency and the lifetime.

If the first plate has three arrays of electrodes, each cell is thentraversed by three electrodes, one from each array, which then form atriad.

The term “gap” is understood to mean the region that separates theelectrodes of each pair or, as the case may be, the regions separatingthe electrodes of each triad. When the width of the coplanar electrodesis constant, the width of the regions separating the electrodes is alsoconstant.

The low-permittivity region located at the top of the barrier ribs maytherefore be discontinuous, that is to say it may be interrupted at thegap separating the coplanar electrodes of each pair by up to 80 μm atmost on either side of the electrode edges, beyond this gap. Thelow-permittivity regions then extend on each side of the gap, especiallyin the discharge expansion regions, that is to say facing the surface ofthe electrodes. The low-permittivity region may extend further, forexample when it is interrupted exactly at the gap separating thecoplanar electrodes.

According to a simpler variant, which is less expensive to manufacture,the succession of low-permittivity regions at the top of each barrierrib forms a continuous low-permittivity region, with no interruption atthe gaps.

According to another variant allowing better control of the dischargeconfinement and greater improvement in the luminous efficiency and thelifetime, at the top of each barrier rib separating two columns, thelow-permittivity regions are discontinuous and interrupted at the gapseparating the electrodes of each pair.

In summary, the subject of the invention is a plasma display panelcomprising an array of barrier ribs each having a base resting on aplate and a top in contact with another plate that includes at least twoarrays of coplanar electrodes, characterized in that these barrier ribshave, at their top, a low-permittivity region with a thickness ofgreater than 3 μm not exceeding one fifth of their total height, whichhas a mean dielectric permittivity at least three times smaller than thedielectric permittivity of these barrier ribs measured at their base.

To further improve the confinement of the sustain discharges far fromthe side walls of the barrier ribs, the invention may also have one ormore of the following features:

-   -   the thickness of said low-permittivity regions is at least equal        to 5 μm;    -   the column separating ribs furthermore have high-permittivity        intermediate regions that are intermediate between the base of        the barrier ribs and said low-permittivity regions and which        have a thickness greater than the thickness of the        low-permittivity regions and a mean dielectric permittivity        greater than the dielectric permittivity of these barrier ribs        measured at their base. Preferably, the mean dielectric        permittivity of these high-permittivity intermediate regions is        not less than five times the dielectric permittivity of the        barrier ribs measured at their base. The succession of        high-permittivity intermediate regions may form continuous        intermediate region of high permittivity. In contrast, at the        top of each barrier rib, the high-permittivity regions may be        discontinuous and interrupted at the gap separating the        electrodes of each pair.

The invention may furthermore include one or more of the followingfeatures:

-   -   the general directions of the coplanar electrodes are        perpendicular to the column separating ribs;    -   the coplanar electrodes Y,Y′ are coated with a dielectric layer        and with a protective/secondary-electron-emissive layer        generally based on magnesia;    -   the second plate includes a third array of electrodes X called        address electrodes, each placed on a column of cells;    -   the array of barrier ribs also includes barrier ribs each        separating two adjacent rows of cells; and    -   the barrier ribs have a height of at least 100 μm.

Documents JP 2000-306517 and JP 07-262930 (see 2nd embodiment associatedwith FIG. 3 of this document) disclose plasma panels in which it is thedielectric layer positioned on the first plate that has low-permittivityregions. In document JP 07-262930, these regions are located between therows of cells and not between the columns, as in the invention. Suchregions make it possible to limit the expansion of the discharges in thevertical direction of the columns, whereas the invention makes itpossible also to limit the expansion of the discharges in the horizontaldirection of the rows. In these two documents, these regions extendcontinuously over the entire width or over the entire useful height ofthe panel and may be in contact with the top of the barrier ribsseparating the columns (FIG. 1 of document JP 2000-306517). It should benoted that such low-permittivity regions are particularly difficult toproduce in the thickness of the dielectric layer, whereas thelow-permittivity regions according to the invention are much easier toproduce at the top of the barrier ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood on reading the descriptionthat follows, given by way of non-limiting example and with reference tothe appended figures in which:

FIGS. 1A and 1B, already described, show a top view and a longitudinalsection respectively, of a cell with coplanar electrodes of constantwidth of a plasma panel according to the prior art;

FIG. 2, already described, shows a top view of a cell with coplanarelectrodes of variable width of a plasma panel according to the priorart;

FIGS. 3 and 4, already described, show the potential distribution in across section on A1-A′1 of one half of a cell of FIG. 1A and in a crosssection on A2-A′2 of one half of a cell of FIG. 2, respectively, at thestart of the application of a 100 V voltage pulse to the coplanarelectrode of this cell half;

FIG. 5 shows a cross-sectional view of a cell of a plasma panelaccording to a first embodiment of the invention;

FIGS. 6 and 7 show two examples of the potential distribution that isobtained in a cross section on A1-A′1 in the half of a cell shown inFIG. 5, using the same conventions as in the case of FIGS. 3 and 4;

FIG. 8 shows a cross sectional view of a cell of a plasma panelaccording to a second embodiment of the invention;

FIGS. 9 and 10 show the potential distribution as obtained in a crosssection on A1-A′1 in the half of a cell shown in FIG. 8 and in a crosssection on A1-A′1 in the half of a cell shown in FIG. 11 respectively,again using the same conventions as in FIGS. 3 and 4;

FIG. 11 shows a cross section of a cell of a plasma panel according to athird embodiment of the invention; and

FIG. 12 shows a variant of the first embodiment of the invention of FIG.5, according to which the top of the barrier ribs includes alow-permittivity region only in the discharge expansion regions.

The figures have not been drawn to scale to as to better reveal certaindetails that will not be clearly apparent if the proportions had beenrespected.

To simplify the description and to bring out the differences andadvantages that the invention affords over the prior art, identicalreferences are used for the elements that provide the same functions.

DESCRIPTION OF PREFERRED EMBODIMENTS

According to the first embodiment of the invention shown in FIG. 5, theplasma panel includes the same elements arranged in the same structureas the panel of the prior art described with reference to FIGS. 1A and1B, the only difference being that the column barrier ribs 15 include abase layer 15 a in contact with the dielectric layer 17 covering thearray of electrodes X of the second plate 12, and a continuous top layer15 b that is applied to the base layer 15 a and extends as far as thedielectric layer 13 and the protective layer 14 covering the arrays ofcoplanar electrodes Y, Y′ of the first plate 11. Here, the coplanarelectrodes each have a constant width over their entire useful length,and the electrode arrays are less expensive to produce and the operationof assembling the plates is not penalized by alignment constraints.

According to this embodiment, the thickness or height D_(a) of the baselayer and the mean dielectric permittivity E_(a) of its constituentmaterial, on the one hand, and the thickness or height D_(b) of the toplayer and the mean dielectric permittivity E_(b) of its constituentmaterial, on the other hand, are adapted so that E_(a) is greater thanE_(b) and for D_(a) to be greater than D_(b), preferably so thatE_(a)≧3E_(b) and that D_(a)≧4D_(b). The top layer therefore correspondsto a continuous low-permittivity region of the barrier ribs. Thethickness of the top layer thus represents at most one fifth of thetotal height of the barrier ribs. To obtain a significant confinementeffect, it is necessary for the thickness of this layer to be greaterthan 3 μm.

As this first embodiment of the invention illustrates, the principle ofthe invention therefore consists in substantially lowering thecapacitance of the column barrier ribs near their top, here over a smallportion D_(b) of the height of these ribs, that is to say near theprotective layer 14 and the dielectric layer 13, over which layers thesustain discharges spread out, so that the electrical capacitance isvery low in the upper portion of these barrier ribs in contact with thecoplanar plate 11 and so that it is higher in the other portion of thesebarrier ribs. This nonuniformity in electrical capacitance of thebarrier ribs specific to the invention allows the equipotential lines inthe low-capacitance region located near the surface of the dielectriclayer and the protective layer covering the coplanar electrodes of theplate 11 to be closer together, and therefore the spreading of thesustain discharges over the dielectric surface are better confined,without “spilling over” onto the side walls of the barrier ribs. Thesmaller the height D_(b) of the top layer compared with the height ofthe base layer D_(a) and the lower the mean dielectric permittivityE_(b) of the top layer compared with the mean dielectric permittivityE_(a) of the base layer, the lower the electrical potential on thedischarge spreading surface near these barrier ribs, by the capacitivedivider effect resulting from the bilayer structure, described above, ofthe barrier ribs.

FIG. 6 shows the distribution of the equipotential lines obtained onthis spreading surface using a discharge cell structure according to thefirst embodiment that has just been described, with E_(a)=3E_(b) andD_(a)=4D_(b), when a 100 V voltage pulse is applied to the electrode Yand when this electrode acts as cathode for this pulse. Thisdistribution corresponds to the potential distribution at the start ofapplication of the pulse, before initiation of the discharge, under thesame assumptions and conventions as in the case of FIGS. 3 and 4described above, the equipotential curves shown as solid linescorresponding to positive potentials and the equipotential curves shownas broken lines corresponding to negative potentials. This FIG. 4 showsthat the degree of confinement of the discharges illustrated by theposition V of the first negative equipotential, shown in broken lines,is close to the case of the prior art described above with reference toFIGS. 2 and 4, where the coplanar electrodes have elements specific toeach cell that are difficult and expensive to produce. Thanks to thisconfinement, at least a comparable improvement in luminous efficiencyand in lifetime of the panel is therefore achieved for a lower cost.

FIG. 7 shows, with the same conventions as in FIG. 6, the distributionof the equipotential lines obtained for a panel according to the firstembodiment in which, this time, E_(a)=5E_(b) and D_(a)=10D_(b). Theposition V of the first negative equipotential is here coincident withthe surface of the dielectric layer and of the protective layer coveringthe electrode Y. During sustained periods, the discharges thereforelonger spread out at all over the side walls of the barrier ribs. Thiscorresponds to the general objective of the invention.

According to a variant of the first embodiment of the invention shown inFIG. 12, the layer 15 b of low permittivity E_(b) is produced at the topof the barrier ribs only near the barrier rib portions that correspondto the discharge expansion region, so that, near the barrier ribportions that correspond to the inter-electrode gap G and near theinitiation region, the top of the barrier ribs has a permittivity E_(a)identical to that of the base layer.

According to this variant, each column separating rib comprises, at itstop and over its entire width, a succession of low-permittivity regions15 b′ that extend on either side of the gap separating the electrodes ofeach pair from a line located at the boundary between the initiationregion Z_(a) and the expansion region Z_(b), to the rear of theinitiating edges 191 of the electrodes of this pair. Conventionally,this boundary line is separated from the initiating edge by at most 80μm. In other words, the width of the initiation region Z_(a) is at most80 μm. These low-permittivity regions have the same thickness and thesame dielectric permittivity as the low-permittivity region describedabove.

As the discharge initiating region is separated from thelow-permittivity barrier rib region, a more uniform electric field overthe entire length of the initiating edges 191 of the electrodes istherefore advantageously obtained. This advantageously makes it possibleto obtain the same ignition properties as in the panels of the prior artdescribed above. In the discharge expansion regions, in which the sidewalls of the barrier ribs run the risk of being subjected to chargedparticles from the discharges, the low-permittivity regions 15 b′according to the invention allow the discharges to be confined, asdescribed above, according to the objective of the invention.

FIG. 8 illustrates, compared with FIG. 5, a second embodiment of theinvention in which the barrier ribs include a continuous upper layer 15c similar to the top layer 15 b described above. This top layer 15 calso has a low thickness D_(c) and a low permittivity E_(c). This toplayer 15 _(c) not only covers, as previously, the top of the barrierribs but extends here, continuously over the entire active surface ofthe second plate 12. Such a configuration is advantageously easier toproduce than that described above, for example using a screen-printingmethod for depositing said top layer. Taking E_(a)=5E_(c) andD_(a)=5D_(c) and under the same conditions as previously, a surfacepotential distribution as shown in FIG. 9 is obtained. This figure showsthat the discharge confinement effect obtained is quite comparable tothat obtained with the embodiment described with reference to FIG. 7. Bycomparing FIGS. 7 and 9, it may be seen that replacing a top layer ofthe barrier ribs with a continuous upper layer coating the entire secondplate does not appreciably modify the distribution of the equipotentiallines so that again the benefits of the invention are obtained.

According to this embodiment, the thickness or height D_(a) of the baselayer and the mean dielectric permittivity E_(a) of its constituentmaterial, on the one hand, and the thickness or height D_(c) of the toplayer and the mean dielectric permittivity E_(c) of its constituentmaterial, on the other hand, are adapted so that E_(a) is greater thanE_(c) and so that D_(a) is greater than D_(c), preferably so thatE_(a)≧3E_(c) and so that D_(a)≧4D_(c). The top layer thereforecorresponds to a low-permittivity region of the barrier ribs. Thethickness of the top layer thus represents at most one fifth of thetotal height of the barrier ribs. To obtain a significant confinementeffect, it is necessary for the thickness of this layer to be greaterthan 3 μm.

In the case of the first and second embodiments, the low-permittivityregion 15 _(b) or 15 _(c) may for example be formed by a porous layer ofaluminum oxide, the remainder of the barrier ribs namely, in this case,the base layer 15 a of higher permittivity being, for example, formedfrom a vitreous layer of lead oxide.

FIG. 11 shows a third embodiment of the invention, which combines thefirst and second embodiments described above. The barrier ribs thereforehave three superposed layers, namely a first, base layer 15 a ofthickness D_(a) and relative permittivity E_(a) resting on thedielectric layer 17 covering the array of electrodes X of the secondplate 12, a second layer 15 c′ of thickness D′_(c) and relativepermittivity E′_(c) covering the entire second plate 12, as in thesecond embodiment, and a third layer 15 b of thickness D_(b) and ofrelative permittivity E_(b) covering only the top of the barrier ribs,as in the first embodiment.

Furthermore according to this third embodiment, E′_(c)>E_(a)>E_(b) andD_(a)>D′_(c)≧D_(b). Preferably, E′_(c)>5E_(a) and E_(a)≧3E_(b), withD_(a)≧4D′_(c) and D′_(c)≧D_(b).

Apart from a low-permittivity region at the top of the barrier ribs, asin the first and second embodiments, is therefore here ahigh-permittivity region inserted between the base of the barrier ribsand this low-permittivity region.

In comparison with the first and second embodiments of the invention,the insertion, into the barrier ribs, of a high-permittivityintermediate region, namely the second layer 15 c′, allows theequipotential lines in the barrier rib region corresponding to the firstlayer 15 a and to the second layer 15 c′ to be moved further apart, insuch a way that the equipotential lines in the third layer 15 b are evenmore closely spaced than previously, thereby improving the confinementof the discharges. E_(b)=E_(a)/5, E′_(c)=5E_(a) andD_(b)=D′_(c)=D_(a)/5, the distribution of the equipotential linesillustrated in FIG. 10, over the half-width of a discharge region, withthe same conventions as previously, is then obtained.

In this third embodiment, the low-permittivity third layer 15 b may forexample be a porous layer of aluminum oxide, the first layer 15 a ofhigher permittivity may be a vitreous layer of lead oxide and the secondlayer 15 c′, corresponding to the low-permittivity intermediate region,may for example be a layer based on TiO₂ or BaTiO₃.

To produce a panel according to the invention in any one of theembodiments that have just been described, suitable materials andmethods known per se to those skilled in the art of plasma panels willbe used.

To operate the plasma panel thus obtained, it is conventional to use astandard plasma panel supply and drive system.

1. A plasma display panel comprising a first plate and a second plateleaving between them a space filled with a discharge gas and partitionedinto a number of discharge cells that are arranged in rows and columns,which also includes an array of insulating barrier ribs comprisingbarrier ribs each separating two adjacent columns of cells and eachhaving a base resting on the said second plate and a top in contact withthe said first plate, this first plate including at least two arrays ofcoplanar electrodes called sustain electrodes, which are oriented alonggeneral directions that are parallel to one another and to the saidrows, which are placed so that each discharge cell is traversed by anelectrode of each array, therefore forming a pair, and which have edgescalled initiation edges which face one another on either side of the gapseparating the electrodes of each pair, wherein each column separationbarrier rib comprises, at its top and over its entire width, asuccession of low-permittivity regions that extend at least on each sideof the gap separating the electrodes of each pair, at least startingfrom a line located 80 μm to the rear of the initiation edges of theelectrodes of this pair, and which have a thickness of greater than 3 μmbut not exceeding one fifth of the total height of the said barrierribs, and a mean dielectric permittivity at least three times smallerthan the dielectric permittivity of the said barrier ribs measured attheir base.
 2. The panel as claimed in claim 1, wherein said coplanarelectrodes each have a constant width over their entire useful length.3. The panel as claimed in claim 1, wherein the succession oflow-permittivity regions at the top of each barrier rib forms acontinuous low-permittivity region.
 4. The panel as claimed in claim 1,wherein, at the top of each barrier rib separating two columns, thelow-permittivity regions are discontinuous and interrupted at the gapseparating the electrodes of each pair.
 5. The panel as claimed in claim1, wherein the thickness of said low-permittivity regions is at leastequal to 5 μm.
 6. The panel as claimed in claim 1, wherein said columnseparating ribs furthermore have high-permittivity intermediate regionsthat are intermediate between the base of the barrier ribs and saidlow-permittivity regions and which have a thickness greater than thethickness of said low-permittivity regions and a mean dielectricpermittivity greater than the dielectric permittivity of said barrierribs measured at their base.
 7. The panel as claimed in claim 1, whereinsaid coplanar electrodes are coated with a dielectric layer and aprotective/secondary-electron-emissive layer.
 8. The panel as claimed inclaim 1, wherein said second plate includes a third array of electrodescalled address electrodes, each placed on a column of cells.
 9. Thepanel as claimed in claim 1, wherein said array of barrier ribs alsoincludes barrier ribs each separating two adjacent rows of cells. 10.The panel as claimed in claim 1, wherein said barrier ribs have a heightof at least 100 μm.